sh-pfc: Don't needlessly check GPIO type in sh_gpio_free()

The GPIO type is always PINMUX_TYPE_FUNCTION when freeing a function
GPIO. Hardcode the type value.

Signed-off-by: Laurent Pinchart <laurent.pinchart+renesas@ideasonboard.com>
Acked-by: Linus Walleij <linus.walleij@linaro.org>